Steven Moffat insists the 'Doctor Who' 50th anniversary episode was "extraordinary difficult" to make because the budget wasn't big enough

The showrunner admits it was "extraordinarily difficult" to create the unique episode - which is being funded by both the BBC and its commercial arm BBC Worldwide - because the production team were given a budget for a 2D project lasting one-hour rather than a feature-length 3D special.

He said "It was unbelievably tough actually making the 50th.

"It was extraordinarily difficult mainly because we were trying to push the boat out and as ever we didn't have enough money. We were making a feature-length 'Doctor Who' on the schedule and budget for an hour. We're doing it in 3D on the budget for 2D.

"[But] you will not see that on screen. It looks amazing."

While Steven is keen to positively promote the episode, he worries about showering the special with superlatives in case die-hard Whovians don't feel the same.

Speaking to sci-fi website Three If By Space, he added: "It's always pressure on 'Doctor Who', it really is. I'm always wary of the episodes where you announce in advance, 'This is a very important episode!' because it's up to the audience.

"I'm very wary of saying this one is really good in advance. I think it's a lot of fun and I think you'll see some stuff you haven't seen before. And you'll see it in three dimensions if you don't mind the headache and glasses."

The 50th anniversary special - which stars Matt Smith as the titular Time Lord as well as David Tennant, Jenna-Louise Coleman, Billie Piper and John Hurt - will air on November 23, exactly 50 years after the show first started in 1963.